Method of determining the receptivity of sheet materials to coatings, inks, and the like



July 18, 1944- B. w. ROWLAND ET AL 2,353,852

METHOD OF DETERMINING THE RECEPTIVITY OF SHEET MATERIALS TO COATINGS, INKS, AND THE LIKE Filed March 7, 1942 2 Sheets-Sheet l B. w. ROWLAND ET AL 2,353,852 METHOD OF DETERMINING THE RECEPTIVITY SHEET MATERIALS TO COATINGS, INKS, AND THE LIKE Filed March '7, 1942 2 Sheets-Sheet 2 m J mk \M. \N 1M1 W x\ w u g 2 I I. W "I e. Z w WILD R \1 l v WW, 2 Z. W er I I MM. 4 4 ..I 2; f0 I w 0, \\\A- v m mN.\ 7 x V I M Rm, hm fi/ mm r MW]? g a m m m a A L \\\\\\\\E a X Ma x wd 7///////////////////////M/////////////// mm \i/ M A WNW f i mm W. KW j 1 $0. 3 bw H f v x MN kw nu W x o o Rm. Q S mm M J I .1 g I l aw x kEZI;zV2zzzzz zzz zwnlMW I w Q V m R\ wm July 18, 1944.

Patented July l8, 1944 METHOD or DETERMINING THE RECEPTIv- ITY OF snEE'rMA'rEnIALs ToooA'rI Gs,

INKS, AND 'rna mm j Ben waRowland, Douglas Fronmuller, and J0- hannes A. Vanv den Akker, Appleton Wis assignors to The Institute of Paper Chemistry, a

. corporation o'twis consin I Application March 7, 1942, Serial No. 433,822

3'Clalms. (cars-s1) I H U a Fig. 6 is an enlarged sectional'view showing the rnepresent invention relates to a testing method for determining andevaluating various surface characteristics 01' sheet materials,- and particularly ofpaper,

In: the past, considerable difllculty has been I experienced in determining the receptivity of Paper and similar products to coating'mate'rials, inks, and the like. Prior to the investigation resulting in the present invention itwas generally believed that unsatisfactory coatings resulted from some inherent defect in the raw stock from whichthe sheet was made. Testing procedures were developed on this theory, but these proved generally unsatisfactory and the only true evaluation of the receptivity characteristics that-could be reached involved applying the actual coating material to the sheet.

In our investigations, directed toward the overcoming of the deficiencies of the prior art testing procedures, we have discovered; that the receptivityv of paper and like sheet materials for coatings, inks, etc., is related to the surface characteristics of such materials, and as will hereinafter appear, we have provided apparatus for accurately evaluating such characteristics to the end that. the receptivity of any particular sheet to coatings, inks,- -etc.', may be determined, even while the sheet is being manufactured, 'The testing ap paratus of our invention is substantially automatic in operation, and-it performs the testing operation with substantially no rubbing or mechanical workingof the surface which isto be tested, an important feature'in view of 'the'relationship which we have found to exist between receptivity to coatings and surface characteristics. Moreover, the apparatus of our-invention is simple and relatively inexpensive; it is rapid and easy to operate; and the results are substantiallyunaffected by the technique of operation; 9

One embodiment of our invention, particularly designed for. evaluating the receptivity. of paper to coating materials and inks, is illustrated in the accompanying drawings and more fullydescribed in the following description. In'the drawings:

Fig. 1 is a perspective view of the complete apparatus; i Fig. 2 isan enlarged sectional view on the general line 2-2 of Fig. 1; 1 a I Fig. 3 isa sectional vlewon line 33 of Fig. 2; Fig; 4 is a'sectional view on the line 4-4 of Fig.3-andshows a bottom plan view of one of the plate elements comprising the doctor or scraper blade'oi the structure shown in Figs. 1 and 3; Fig. 5 is a top plan view of the other element forming th'e'doctor'blade;

operationof the doctor'blade; and

Fig; 7 isan 'enlargedsectional view of the fluid trap forming .a part of the'apparatus. v Reduced'to its basic elements the testing apparatus of the present invention comprises means, including a resilient'platen', for hol'ding the sheet of paper or other material to be tested substantially flat, and means including a. vacuum doctor or scraper mechanism for advancing a quantity of a suitable testing fluidacross the surface of the sheet and for immediately thereafter rem'ov .ing any excess from the surface oi such sheet. In the particular embodiment illustrated in the drawings, this latter means includes an electric" motor or other 'app'aratus'fo'r moving thedocto'r' form, relatively high speed. More specifically, the apparatus includes asuitable base I l of wood or metal provided with a'pair of rigid uprights III which serve as thesupport means for a pair of spaced, parallel guide rails ll. The operating and support means for the'vacuuin mechanism across-the sheet beingtestedat a uni- "doctor' blade mechanism comprises afrel'atively I heavy, metallic plate ll'having-a pair oi'spaced,

parallel grooves is cut therein, l for 'slidably en-'- gaging the guide rails-Ii; The platen supp rt f r the sample includes a sheetoiplateglulssi II of suitable dimensions which' is positioned onthe main base l'l inthe area beneath the guide rails I I and a spring operated, press clip "for holding. the sample. 2 i

' To provide a resilient'support for thesample, a flat'pad or cushion 25 of uniform thickness is disposed on top of the glass plate 21. The resilient pad may comprise aiplurality oisuperposed sheets of paper. or a sheet of rubber or other material, and should be located between the sample and the plate 2! during theoperation of the apparatus. In one particularly satisfactory embodiment of the invention zthe glass plate llyhas a width of: about 5 inches and a length of approximately 15 inches. .The resilient pad 25in this-embodiment is about one-eighth inch thick and comprises approximately twentysheets of a rela- I I tively hard paper.

The supporting plate H for the vacuum 'doctor mechanism is moved longitudinally of the apparatus by means of an electric motor 21, abelt '2! which extends through suitable openings 3| .in'the uprights l3, a fixed pulley 3 3, and a'm'otor pulley 34 about-which the belt is wrapped once around.

In the interest of smooth, quick starting, a spring 36 is preferably interposedin the belt circuit.

I A start and stop switch as for the motor?! is supported on the right hand upright I3 and is connected into the electrical circuit for the motor in conventional manner. In the particular apparatus shown in the drawings, the plate 11 and the doctor blade mechanism which is supported thereon are returned to the initial operatlng position by hand. It will be understood, however, that a mechanical return can beused if desired, as for example, by providing a reversing motor.

The motor switch 38 is so arranged that it automatically shuts off the motor 21 when the supporting plate l1 approaches the right hand end of the apparatus during the operation of the machine. 1

In the illustrated device, the vacuunr doctor blade mechanism includes a two element doctor paratus illustrated in the drawings, this reduced pressure is provided by means of a Venturi aspreferably connected intothe tubing 69, and under blade 35 which is hingedly supported on the main plate I1 by means of a support arm 31 and .a

U-shaped spring hinge 39. The spring hinge. 39

includes adjustable tension springs 41 which serve to. biasthe doctor blade'in the direction of the sample support means. The-support arm 31 which provides the mechanical connection between the spring hinge 39 and the two element doctor blade 35 is integrally attached at one end to the lower elements 43 of the doctor blade and is threaded at the other. end for engagement with a suitable threaded block 45 integrally attached to the lower element of the hinge 39.,It will be apparent that the angle of the doctor blade relative to the plane of the sample support can be readily adjusted by screwing the supporting arm 31 in or out of the threaded block element 45. i U

The two elements. of the doctor blade 35 are, particularly shownin Figs. 4, 5, and 6. The lower element 43 has a beveled under'surface 41 which .The upper doctor blade element 5|, is shown in bottom plan view in Fig; 4 and comprises a metallic plate-whichis cutaway on its under. surface as illustrated at 53in;F,igs. 4 and 6., When the two elements 43 and, 5| are assembled, this cut away portion 53p'rovides an outwardly flaring,

normal operating conditions, it will be found advisable to adjust the vacuum within the chamber 55 to about to centimeters of mercury below atmospheric.

A substantial amount of liquid is drawn into the vacuum chamber 55 during the operation of the Preferably, the trap 1| should be of glass to permit visual examination, andit should be so designed that, it includes spaced entranceand exit passageways 19 and 81, asillustrated in Fig. '1. It is desirable that the level of the, exit passageway 8I shall be below the level of the entrance passageway 19 to minimize sudden chan es in pressure. To facilitate cleaning, oneend of the trap may be left open and sealed with a rubber. cap 83. In some instances, it may be desirable to provide vanes or bafiies within the vacuum chamher as indicated by the dotted lines 85 .in Fig. 4, forthe purpo'se'of equalizing fluid flow therein. Generally, however, thesevanes are unnecessary.

The preferred testing procedure includes the following steps: A sample of the paper or other material to be tested is fastened in place on the sample supporting pad by the spring clip 23, as illustrated at 81. The sample 81 should have a width-greater than the width of the doctor blade and a length atleast equal to the length of the travel of the doctor blade. Byvirtue of the springhinge connection between the doctor blade '35 andthe support and operating means therefor, the doctor blade can .be readily lifted to vacuum chamber which extends alongsubstantially the entire .width of the doctor blade.

The upper element 5| is adjusta-bly fastened to the lower element-43 by means of suitable screws 51, which. engage threaded openings 59in the lower element and which pass through slotted openings-6| in" the-upper element. The lower surfacesof the end edge portions 63 of the upper element 5| are, beveled to thesame angle as the surface 410i the lower element 43 in order, that the doctor blade may restfiat against the sample being tested. The'engaging surfaces of the two elements 41 and 5| are preferably ground to a very close fit, and for best. results it is highly desirable that the bevel surfaces 41 and 63 which contact t-he'sample shall be perfectly flat. In one particularly satisfactory embodiment of the invention the doctor blade had a total width of approximately 7.0 cm. and a width at the beveled porbelieved desirable. Subatmospheric pressure is maintained 'within the vacuum chamber 55 during the operation'of the apparatus by the use of any suitable mechanism. In the particular aption of about .7 cm. Approximately this ratio isv permit the sample to be put into place.

Before starting the test, the doctor blade 35 and its operating mechanism are moved to the extreme left hand position, ,as'shown in Fig. 1. Also before starting the test the aspirator65- or other vacuum' producing apparatus must be turned on, as by.operation ofthe valve 61, and the pressure within'the vacuum chamber 55 of the doctor blade structure 35 adjusted to the desiredvalue. As stated previously in making tests to determine the receptivity of paper to coating materials,.best results are obtained with a pressure in the vacuum chamber. of about 15 to 20 centimeters of mercury below atmospheric. 'With the apparatus in'the starting position, as described, a quantity-of the testing fluid is applied, by means of a medicine dropper or otherwise, to form a pool of liquid 89 (Fig. 6) directly ahead of the doctor blade 35, as illustrated in Fig. 6. Thereupon, the motor switch 39 is operated to effect the energization of the motor 21 which moves'the' doctor blade mechanism. at relatively 7 high speed from the position illustrated in full in Fig.3 to' the position illustrated in dotted lines in that figure. This movement of the 'doctor blade mechanism, in combination with the doc-. toringaction resulting from the vacuum which is maintained within the chamber 55 causes a very thin coating of the testing material to be spread over the surface of the sample beingtested in a very short interval of time. Speeds of'the order of about 20 to 30 inches per second have been used with very good results. This coating will form patterns which can be readily evaluated as a measure of the receptivity of the sheet to coating materials. If the pattern is uniform and continuous, the material has a high degree of receptivity for the coating materials, and particularly for those coating materials which comprise a mixture of an adhesive. such as casein or starch, and a pigment, such as clay, satin white or some other of the known-coating pigments. If the pattern is discontinuous and contains fish eyes or other irregularities, difficulty in coating may be expected, the amount of difllculty being directly proportional to the amount of discontinuance in the pattern. Comparative,reference standards may be set up for any particular test or series of tests. By virtue of the fact that the liquid testin material is applied ahead of the doctor working of the surface of the sample, which might tend to give erroneous indications of the receptivity of the surface to coating. In the described -embodiment, pressures areusedof the order of 100 grams total across the entire conv tact area of the doctor blade, and while some variation in this pressure may be permissible, best results appear to be obtained with approxi mately this pressure. The period of time required to make tests by use of the apparatus of the present invention is so short that close control of the actual manufacture operation is made possible in the case of paper and like materials.

As stated previously, the test may be, used not only for determining the receptivity of sheet material to coating, but also the receptivity of previously coated sheets to ink,.or to other liquids. In these instances, use of some different type of testing fluid may be indicated. For determining coatability, we prefer to use an aqueous, colored medium, preferably a colloid, although in some instances ordinary suspensions have proven satisfactory. For other tests, other testing liquids of greater or less viscosity may be desirable and the term fluid testing material" as used herein is intended for all such materials.

It will be apparent that various other devices embodying the principles disclosed in the foregoing may be developed by those skilled in the art. Accordingly, it is desired that the accompanying claims shall be given the broadest reasonable construction consistent with the language appearing therein and the prior art.

' We claim:

1. The method of determining the receptivity of sheet material to coatings, inks, and the like which consists in supporting a sample of the i material to be tested on a suitable, resilient sur-.

' ing materialas is possible from the surface of the sample by use of a suction current, thereby effecting-the very rapid application of a very thin coating of the testing material to the surface of the sample, the said application of .testing material being carried out without substantial mechanical working of the surface of the sample, and finally evaluating the resultin pattern by comparison with known standards.

2. The method of determining the receptivity of sheet material to coatings, inks, and the like which consists in supporting a sample of the material to be tested on a suitable, resilient surface, applying a substantial quantity of a fluid testing material to a restricted area of the sample, spreading said fluid testing material over the sample at a speed which is of the order of about 20 to 30 inches per second, while immediately doctoring off as much of the spread testing material as is'possible from the surface of the sample by the use of a suction current of the order of about 15 to 20 centimeters of mercury, thereby effecting the very rapid application of a very thin coating of the testing material to thesurface of the sample, the said application of te'st-' ing material being carried out without substantial mechanical working of the sample, and finally evaluating the resultant pattern by comparison with known standards.

3. The method of determining the receptivity of sheet material to coatings, inks, and the like which consists in applying a substantial quantity of a fluid testing material to a restricted area of the sample, spreading said fluid testing material over the sample at relatively high speed, while immediately doctoring oil as much of the spread testing material as'is possible from the surface of the sample by use of a suction cur rent, thereby effecting the very rapid application of a very thin coating of the testing material to the surface of the sample, the said application BEN W. ROWLAND. DOUGLAS FRONMULLER. JOHANNES A. VAN new AKKER. 

